Switching power supply or converter topology using a boost circuit is known in the art and is a basic technology for many applications. However, certain limitations are encountered when practical designs are implemented. For example, although it is common to use boost circuits to generate voltages, the resulting limited power output capacity prevents the most efficient use of the boost circuits. Typically, then, concerns relating to power density, component stresses, and efficiency are compromised.
An inductor boost circuit is usually operated in one of two regions or modes of operation. These regions are commonly known as discontinuous and continuous modes. These terms relate to the type of current present in the inductor during operation. With the continuous mode, there is continuous current (DC) in the inductor; whereas with the discontinuous mode, there are times when there is no current passing through the inductor. The continuous mode necessitates a larger inductor and more inductor core losses than would be necessary if the discontinuous mode were used. However, the discontinuous mode causes higher peak ripple currents through components at a given power output. The power output of a single boost circuit is typically limited to 100 watts in practical designs.
There are advantages and disadvantages to both the continuous and discontinuous modes. For example, an advantage to using the continuous mode is that it can produce a greater output power. However, the continuous mode is disadvantageous in that it is less efficient than the discontinuous mode, and is subject to subharmonic oscillations, depending on the current duty cycle and the inductor size. While the discontinuous mode is more efficient, it causes higher peak current and has a lower output power, as compared to the continuous mode. If the power output of a discontinuous mode is increased, the peak or ripple currents become increasingly stressful to the circuit components.
In the prior art, a multi-stage technique is used to control or enhance the power factor of the AC input power, as described in U.S. Pat. Nos. 4,982,148 and 4,600,982. Unfortunately, the techniques described in the prior art do not sufficiently address the enhancement of efficiency and the reduction of relative peak or ripple currents in components.
It is seen then that there exists a need for a means of reducing ripple current which overcomes the problems of power output loss and decreased efficiency encountered in the prior art.